1. Field of the Invention
This invention relates generally to a method for forming and exploiting fields, e.g., magnetic fields; at the interfaces between components of a composite material, the composite material itself and devices which incorporate the material such as electrochemical systems and separators, including fuel cells, batteries, and separations resulting in enhanced and modified flux and performance. The invention also relates to apparatus, methods of making and methods of using interfacial fields for the separation of transition metals, electrolytic applications such as fuel cells, electrolysis involving free radical products and intermediates, and biological systems.
2. Background of the Related Art
The following discussion provides a brief overview of the current understanding of magnetic properties in composites.
Magnetic field effects on chemical systems can be divided into several types, including electron transfer (kinetic), mass transport, and thermodynamic. Magnetic effects on homogeneous solutions for electron transfer have been discussed in the background literature, and substantial background research has been conducted on the magnetic effects on mass transport in solutions. Kinetically, reaction rates, reaction pathways, and product distributions can be altered. Macroscopic thermodynamic effects are generally negligible.
(A) Electron Transfer
In electron transfer reactions, an electron is transferred between a molecule or an ion. Electron transfer reactions are ubiquitous throughout natural and technological systems, including biological energy production, ozone depletion, and technologies from photography through batteries, solar cells, fuel cells, and corrosion. Understanding the speed or rates of electron transfer reactions is fundamentally important, since controlling rates can decrease energy consumption, lead to more efficient technologies, and reduce environmental load. For example, approximately 6% of domestic electrical power is used in the chloralkali industry for production of basic chemical stocks, such as hydrochloric acid, sulfuric acid, chlorine gas and sodium hydroxide. Electrochemical refining of aluminum uses a similar amount of power. Any improvement in electron transfer rates for various industrial reactions would significantly reduce energy consumption. Another example involves a fuel cell, which generates power electrically from a fuel (e.g., hydrogen or alcohol) while producing significantly less pollution than an internal combustion engine.
Electron transfer reactions can be characterized as either homogenous or heterogeneous. If the reaction occurs in a single phase (i.e., solid, liquid or gas) between two ions or molecules, the reaction can be characterized as a homogenous electron transfer. Consider two chemically distinct ions, Az and By, where z and y are the charges of the species. Az and By undergo a homogeneous electron transfer reaction as:
Az+ByAzxc2x11+By∓1.xe2x80x83xe2x80x83(1)
FIG. 1 shows a homogeneous electron transfer where an electron e transferred from one ion Az to another ion By forms the products Az+1, Byxe2x88x921. All ions are in solution.
When two different charge states of the same ion undergo homogeneous electron transfer, a self exchange reaction occurs as follows:
Az+1+AzAz+Az+1.xe2x80x83xe2x80x83(2)
While the effects of magnetic fields on homogeneous electron transfer reactions are well-known, little is known about magnetic field effects on heterogeneous reactions due to a lack of sound experimental data and theory.
Electron transfer reaction theory has developed since the 1950s. A model for homogeneous reactions was developed and later modified to describe heterogeneous reactions. Marcus received the Nobel prize in 1991 for theoretical description of those processes based on transition state theory. While the mathematics of Marcus"" original theory were done with pencil and paper, the theory has evolved to include quantum mechanical descriptions resolved using sophisticated computer programs.
(B) Mass Transport
Magnetically driven mass transport effects have been studied in electrochemical cells positioned between the poles of large magnets. Effects vary depending on the orientation of the electrode, the relative orientation of the magnetic field and the electrode, forced or natural convection, and the relative concentrations of the redox species and electrolyte.
Paramagnetic molecules have unpaired electrons and are attracted into a magnetic field, while diamagnetic species of molecules possess paired electrons and are slightly repelled by the field. While radicals and oxygen are paramagnetic, most organic molecules are diamagnetic, and metal ions and transition metal complexes can be either para- or diamagnetic. The magnitude of the response of a molecule or species in a solution or fluid to a magnetic field can be parameterized by the molar magnetic susceptibility, "khgr"m (cm3/mole). For diamagnetic species, "khgr"m is between about (xe2x88x921 to xe2x88x92500)xc3x9710xe2x88x926 cm3/mole, and temperature-independent. For paramagnetic species, "khgr"m ranges from 0 to +0.01 cm3/mole and, once corrected for its usually small diamagnetic component, varies inversely with temperature in accordance with Curie""s Law. Because electrochemistry tends to involve single electron transfer events, the majority of electrochemical reactions should result in a net change in the magnetic susceptibility of species near the electrode.
While ions are monopoles that move either with or against an electric field, depending on the charge of the ion, paramagnetic species are dipoles and will always be aligned in a magnetic field, independent of the direction of the magnetic vector. Those dipoles will experience a net magnetic force if a field gradient exists.
(C) Thermodynamics
A uniformly applied magnetic field created by placing a solution between the poles of a magnet will have a negligible effect on the free energy of reaction. The change in the free energy of the reaction, xcex94Gm, is shown as xcex94Gm=xe2x88x920.5xcex94"khgr"mB2 J/mole, where xcex94"khgr"m is the difference in magnetic susceptibility of the products and reactants and B is the magnetic induction in Gauss. For the conversion of a diamagnetic species into a paramagnetic species, xcex94"khgr"mxe2x89xa60.01 cm3/mole. In an applied magnetic field of 1 Tesla (T), where 1 Telsa=10 k Gauss, |xcex94Gm|xe2x89xa60.05 J/mole. Even in the strongest laboratory fields of 10 T, the effect is negligible compared to typical free energies of reaction.
However, while the macroscopic effects are negligible when the magnet is placed external to the cell and a uniform field is applied to the solution, substantial microscopic effects may exist. The above-discussed effects are most significant in local fields of composites, and in molecules in composites within a short distance of the source of the magnetic field. For example, for a magnetic wire or cylinder, the magnetic field decreases over a distance, x, as xxe2x88x923. Thus the field experienced by a molecule 1 nm from the magnet may be roughly 1021 times greater than the field experienced at 1 cm.
The basic objective of a fuel cell is to allow a reaction between a fuel (e.g., hydrogen) and an oxidant (e.g., oxygen) which normally react spontaneously (and often violently) to discharge in a controlled manner. By containing the fuel and oxidant at separate electrodes, the discharge of the reaction is electrical rather than thermal. A wire coupling the electrodes captures the current and voltage of the discharging system, thus providing power to drive an external device, such as an electric motor.
Fuel cells combine the best characteristics of a battery and a combustion engine. Similar to the combustion engine, they are not recharged electrically and output power as long as fuel is provided. Similar to the battery, fuel cells are electrical devices capable of providing power and are theoretically not subject to a combustion engine""s Carnot limitations. The expansion and contraction of pistons limits heat engines to about 40% theoretical power efficiency and about 25% practical efficiency under optimal conditions. In contrast, fuel cells approach 100% efficiency in theory, and have been demonstrated to operate at better than 90% efficiency.
Fuel cells are most commonly characterized by their operating temperature and by the fuel and oxidant which power them. High temperature fuel cells, such as molten carbonate and solid oxide fuel cells, operate at several hundred degrees centigrade, and are practical for large-scale power generation. For smaller, more portable power demands, such as automobiles, low temperature fuel cells operate at or below about 100xc2x0 C.
Proton exchange membrane (PEM) fuel cells are the most common example of low temperature fuel cells. In PEM fuel cells, oxygen or atmospheric air serves as the oxidant and hydrogen typically serves as the fuel. A cell based on hydrogen and oxygen is denoted as H2/O2, where the convention is fuel/oxidant.
FIG. 2 illustrates a PEM fuel cell. The PEM fuel cell employs hydrogen (H2) as a feed for an anode (10) and oxygen (O2) in air as a feed for a cathode (12). Those fuels decompose electrolytically to yield water at the cathode. Both anode and cathode are typically modified with a noble metal catalyst, for example, platinum (Pt). The hydrogen and oxygen are separated by a proton exchange membrane 14 (such as Nafion) to prevent thermal decomposition of the fuels at the noble metal catalyst. The reactions at the cathode 12 and anode 10 can be summarized as follows:                     Cathode                            Anode                                      Net          ⁢                      xe2x80x83                    ⁢          Reaction                      ⁢                                                        O              2                        +                          4              ⁢                              xe2x80x83                            ⁢                              H                +                                      +                          4              ⁢              e                                ⇌                      xe2x80x83                    ⁢                      2            ⁢                          xe2x80x83                        ⁢                          H              2                        ⁢            O                                                                                  2              ⁢                              H                +                                      +                          2              ⁢              e                                ⇌                                    xe2x80x83                        ⁢                          xe2x80x83                                ⁢                      H            2                                                                                  O              2                        +                          2              ⁢                              xe2x80x83                            ⁢                              H                2                                              ⁢                      xe2x80x83                    ⇌                      xe2x80x83                    ⁢                      2            ⁢                          xe2x80x83                        ⁢                          H              2                        ⁢            O                                ⁢      xe2x80x83    ⁢                                          E            cathode            ∘                    =                      1.23            ⁢                          xe2x80x83                        ⁢            V                                                                    E            anode            ∘                    ⁢                      xe2x80x83                    =                      0.00            ⁢                          xe2x80x83                        ⁢            V                                                                    E            cell            ∘                    ⁢                      xe2x80x83                    =                      1.23            ⁢                          xe2x80x83                        ⁢            V                                ⁢      xe2x80x83    ⁢                              (          3          )                                              (          4          )                                              (          5          )                    
However, a fuel cell typically runs under non-equilibrium conditions and is thus subject to kinetic limitations. Usually, the majority of the kinetic limitations are at the cathode 12:
O2+4H++4e2H2O Exc2x0cathode=1.23Vxe2x80x83xe2x80x83(6)
As the cathode reaction becomes increasingly kinetically limited, the cell voltage drops and a second reaction path, the two electron/two proton reduction of oxygen to peroxide, becomes increasingly favored. The second reaction path consumes oxygen in two electron steps with lower thermodynamic potential as follows:
xe2x80x83O2+2H++2eH2O2 Exc2x0H2O2=0.68Vxe2x80x83xe2x80x83(7)
The standard free energy of the reaction in equation (7) is 30% of the free energy available from the four electron reduction of oxygen to water shown in Equation (6). The decrease in current associated with the decreased number of electrons transferred, combined with the decreased cell potential, yields a substantially lower fuel cell power output.
The cathode reaction efficiency can be enhanced by increasing the concentration or pressure and flow rate of the feeds to the cathode 12 (i.e., protons and oxygen) to enhance the flux (i.e., the reaction rate at the cathode 12 in moles/cm2sxe2x88x921). The proton flux is readily maintained at a sufficiently high value by the proton exchange membrane 14 (e.g., Nafion) to meet the demand set by the cathode reaction. Normally, the flux is enhanced and the reaction is biased to favor the formation of water by pressurizing the air feed to the cathode 12. Typically, pressures of at least 5 to 10 atmospheres are required.
At least three major impediments prevent large-scale commercialization of PEM fuel cell technology. First, the kinetics for hydrogen oxidation in an H2/O2 fuel cell are very rapid compared to the kinetics of oxygen reduction. To overcome the kinetic limitations of oxygen, the cathode 12 is pressurized to roughly five times the anode pressure. The resulting change in the oxygen concentration at the cathode 12 shifts the reaction toward the desired electrolysis product, which is water. In a fuel cell that substitutes air for oxygen, pressurization sweeps out the inert nitrogen, which can build up in the cathode 12, and reduces the local partial pressure of oxygen. Unfortunately, the pumps required to pressurize the cathode 12 cause a parasitic power loss of approximately 15% and significantly increase the weight and noise of the fuel cell. The moving parts of the pumps also increase the complexity and the number of failure mechanisms of the system. As a result, pumps are particularly disadvantageous for portable applications.
A second impediment is that hydrogen is not the most convenient fuel, given its exothermic (flammable and explosive) reactivity with oxygen. Indirect reformation of organic fuels over, for example, a hot, copper and zinc catalyst to yield hydrogen to feed the fuel cell, is an alternative fuel source. Direct reformation, where the fuel is fed directly to the anode 10, is the optimal method for using organic fuels. However, the problem of electrode passivation with by-products such as carbon monoxide remains.
A third impediment is that feeding an organic fuel directly into the anode 10 creates a secondary complexity. The separator 14 tends to imbibe organic fuels, which cross the membrane to the cathode 12 and react directly with the oxidant in the presence of the catalyst. The direct reaction short circuits the electron flow through the external circuit and reduces the fuel cell power output. Even with hydrogen fuel cells, significant power losses occur when the proton carries too much water from the anode 10 to the cathode 12, because the anode 10 dries and the cathode 12 floods. This is commonly known as crossover.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
It is therefore an object of the invention to provide an improved electrode.
Another object of the invention is to provide a coating on an electrode to enhance the flux of magnetizable species to and from the electrode.
Another object of the invention is to provide a separator to separate magnetic species from each other dependent upon magnetic susceptibility.
Another object of the invention is to provide a method for making a coating for an electrode to improve the flux of magnetizable species to and from the electrode.
Another object of the invention is to provide a method for coating a surface of a device with a magnetic composite material responsive to an external magnetic field.
Another object of the invention is to provide an improved fuel cell.
Another object of the invention is to provide an improved cathode in a fuel cell.
Another object of the invention is to provide an improved anode in a fuel cell.
Another object of the invention is to provide an improved battery.
Another object of the invention is to provide an improved flux switch.
Another object of the invention is to provide an improved electrolytic cell.
Another object of the invention is to provide an improved electrolytic cell for an electrolyzable gas.
Another object of the invention is to provide an improved electrode for direct reformation of liquid or gaseous fuels.
Another object of the invention is to provide an electrochemical cell having improved power generation and/or synthetic capability.
Another object of the invention is to provide a method for coating the surface of an electrode, wherein the electrode allows direct reformation of a liquid or gaseous fuel.
Another object of the present invention is to develop experimental systems to simplify investigation of and to facilitate heterogeneous and homogeneous electron transfer in a magnetic field.
Another object of the present invention is to extend the models and broaden the application of simple heterogeneous and homogeneous electron transfer in a magnetic field to include the adsorption and solution phase chemical steps often important in real systems.
One advantage of the invention is that it can enhance the flux of paramagnetic species to an electrode.
Another advantage of the invention is that it can enhance the flux of oxygen to the cathode in a fuel cell, equivalent to passive pressurization.
Another advantage of the invention is that it can separate paramagnetic, diamagnetic, and nonmagnetic chemical species from a mixture.
Another advantage of the invention is that it can separate chemical species according to chemical, viscosity, and magnetic properties.
Another advantage of the invention is that it can take advantage of magnetic field gradients in magnetic composites.
Another advantage of the invention is that it can be designed to work with internal or external magnetic fields, or both.
Another advantage of the invention is that it establishes magnetic fields at the surface of an electrode.
Another advantage of the invention is that it stabilizes free radicals generated during the electrolysis process.
Another advantage of the invention is that it allows the choice of alteration of the product distribution.
Another advantage of the invention is that, unlike thermal energy sources such as engines and generators, electrical devices such as batteries and fuel cells are not saddled with thermodynamic constraints (Carnot limitations) including thermal efficiencies of about 40% theoretical maximum and about 25% practical efficiency, and therefore, electrical devices such as fuel cells can exhibit 100% maximum and 90% practical efficiency.
Another advantage of the invention is that PEM fuel cells run at temperatures below about 100xc2x0 C.
Another advantage of the invention is that PEM fuel cells give higher power per area and can reduce weight, thus reducing size and heat transfer problems.
Another advantage of the invention is that fuel cells can be designed with constant power and scalable current-voltage characteristics, because the fuel cell can be built as a set of patch cells on a single membrane and those cells can be interconnected in series or parallel such that a single fuel cell device could serve as a power source to a variety of devices, and higher current is provided by connecting more cells in parallel, and higher voltage is provided by connecting more cells in series.
Another advantage of the invention is that fuel cells are inherently simple devices with no moving parts, and the need for replacement parts and the likelihood of mechanical failure of a fuel cell are much lower than that of mechanical devices, such as engines and generators.
Another advantage of the invention is that PEM fuel cells are conformable and can be designed as flexible thin packages. For example, a package resembling an overhead transparency in plastic bag would provide sufficient power to run a laptop.
Another advantage of the invention is that PEM fuel cells without pumps weigh less than batteries, and are significantly lighter than engines and generators.
Another advantage of the invention is that PEM fuel cells occupy less volume than an engine or generator for approximately the same power output, and the volume is conformable.
Another advantage of the invention is that PEM fuel cells without pumps make no noise.
Another advantage of the invention is that PEM fuel cells are based on polymeric materials and platinized carbon and thus produce little or no toxicity or environmental risk as compared to batteries.
Another advantage of the invention is that because the PEM fuel cell is a device to convert fuel to energy and, as a battery is a container to hold energy, a less extensive supply line is needed to provide fuel alone instead of disposable battery packages.
Another advantage of the invention is that because fuels such as hydrogen, methanol or gasoline have high energy densities (energy per weight), fuel cells provide a higher power density (power per weight) than batteries and, with current technologies providing energy densities of 50 W/kg, hydrogen/air fuel cells provide a power density of about 400 W/kg.
Another advantage of the invention is a three-fold improvement in power with magnetic modification.
Another advantage of the invention is that fuel cells can run constantly as long as fuel and oxygen are provided. They can also be turned on and off for intermittent use.
One feature of the invention is that it includes a magnetically modified electrode.
Another feature of the invention is that it includes an electrochemical cell having at least one electrode with a magnetic composite material disposed on the surface thereof, wherein the electrochemical cell provides enhanced power generation and/or synthetic capability.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.